A cutting insert of the kind in question is a replaceable wear part for detachable mounting in a holder, which may have a number of alternative shapes, and may be used industrially for most varying purposes, such as milling, drilling, reaming, turning and the like. The workpieces machined are usually made of metal, the cutting inserts being manufactured from a hard, wear-resistant material, such as cemented carbide, silicon nitride, aluminum oxide, etc., while the insert holders are manufactured from a more elastic material, in particular steel.
The cutting insert may have two opposite, first and second surfaces, at least one of which forms a chip-removal surface. The chip-removal surface is a surface over at least a part of which a chip can slide when using the cutting insert. The chip-removal surface may be a so-called cutting-geometry surface having a particular, topographic design with a purpose of, in a way known per se in the art, carrying away and breaking off chips formed in the machining of the workpiece. One or more side surfaces extend between the first and second surfaces. In case that only the first surface is a chip-removal surface (a so-called single-sided cutting insert), the second surface is only an abutment surface for support against the holder, and in case both the first and the second surface are a chip-removal surface (a so-called double-sided cutting insert), both the first and the second surface may at least partly serve also as an abutment surface.
As seen with the chip-removal surface facing the observer, the cutting insert may have alternative shapes, e.g., a round, in particular a circular or oval shape, or a polygonal shape. In a polygonal shape, the cutting insert has a side surface having at least three usually plane or slightly arched main portions, here denominated main-surface portions, wherein adjacent main-surface portions transform into each other via a convexly rounded nose, here also denominated transition-surface portion, to which at least one cutting edge connects, formed between the chip-removal surface and the transition-surface portion. Such a cutting edge may be said to have a main-edge segment that, in use, carries out the major part of the chip-removing operation. Via at least one portion of the nose, the main-edge segment extends to a surface-wiping edge segment, in this description also called wiping-edge segment, that, in use, wipes off and levels the machined surface of the workpiece. The wiping-edge segment extends to an additional segment that is arranged to clear at a certain clearance angle from a machined surface of the workpiece. In polygonal cutting inserts, such a wiping-edge segment may be present on one side of the proper nose (asymmetrical nose) or on both sides of the nose (symmetrical nose).
The surface finish of the rotating workpiece is affected by the interaction between the design of the cutting edge and the feed. In this respect, the wiping-edge segment is particularly important. In previously known turning inserts (see, for instance, International Patent Application Publication No. WO95/00272, U.S. Pat. Nos. 6,217,263, 5,226,761, Swedish Patent No. 9401732-4, Swedish Patent No. 9702501-9 and SU1782196), the wiping-edge segment is usually arched, and the length thereof is essentially as great as the feed. A tangential point is defined by the point of the cutting edge that in use is closest to the rotation axis of the workpiece. A troublesome circumstance for the surface finish in previously known cutting inserts is that the location of the actual tangential point along the wiping-edge segment has not been able to be predetermined. Thus, the true tangential point may “drift” in a uncontrollable way between the two opposite ends of the wiping-edge segment, depending on the alignment of the cutting insert in relation to the workpiece, and in this connection give rise to varying surface finish.
European Patent No. 1297921A presents a cutting insert that solves the problem of the “drifting” of the tangential point and that affords a considerably better control of the surface finish. However, even if European Patent No. 1297921A has achieved an improvement in cutting inserts of the kind in question, there remains a need for further improving the surface finish.
In addition, there is a need in known cutting inserts for decreasing cutting forces and vibrations, as well as increasing the service life of the cutting insert.
An object of the invention is to provide a cutting insert that generally ensures improved surface finish of the machined surface of a workpiece. In its materialization in the form of turning inserts, it should be possible to utilize this possibility, for instance for radically increased feed with retained or even improved surface finish, and alternatively improved surface finish at unaltered feed.
Additional objects of the invention are to decrease cutting forces, to decrease vibrations, as well as to increase the service life of the cutting insert.
The invention may be used for general increase of the performance of cutting inserts provided with wiping-edge segments but intended for other machining techniques than turning, such as milling, drilling, reaming or the like.